Herpes simplex virus type 2 (HSV-2) is the major cause of genital herpes, one of the most frequent sexually transmitted diseases. With an estimated US seroprevalence rate of 17% among 14-49 years olds, and the recognition of genital herpes as a worldwide pandemic, the development of strategies to prevent HSV infection is at the forefront of herpes research. The initial site of exposure to herpes simplex virus type 2 (HSV-2) during viral transmission occurs in the genital tract typically during asymptomatic HSV shedding from infected sexual partners. In order to gain insight into the correlates of HSV-2 protection at the genital mucosa, we propose to investigate potential innate immune mechanisms of HSV-2 resistance among subjects seronegative for HSV-1 and HSV-2 (HSVneg) who are frequently exposed to HSV-2 from infected sexual partners. We have recently characterized 2 distinct groups of HSVneg subjects: (1) Immune Seronegative (IS), include HSVneg subjects with previous or current histories of HSV exposure from infected sexual partners and who possess HSV- specific T cell responses;(2) Exposed Seronegative (ES), include HSVneg subjects who are in long-standing HSV-discordant sexual relationships with HSV-2 infected partners and who lack HSV-specific T cell responses. Our working hypothesis is that ES subjects exposed to HSV-2 from infected sexual partners have an effective innate immune response that results in an abortive infection and insufficient viral antigen presentation to generate a T cell response to HSV-2 . IS subjects exposed to HSV-2 from infected sexual partners have an incomplete block of viral infection by innate immune responses and thus there is sufficient HSV replication and antigen presentation to promote a T cell response which clears the infection before latency can be established. HSV-2 infected subjects lack effective innate and adaptive immune mechanisms to prevent primary HSV-2 infection and latency. Therefore, the overall goal of this proposal is to determine if there is a hierarchy of innate immune resistance to genital mucosal infection by HSV-2 in ES versus IS versus HSV-2-infected subjects. We will determine if ES subjects have greater constitutive anti-HSV-2 activity at the genital mucosa compared to IS and HSV-2 infected subjects. Genital mucosal samples will be obtained from ES, IS and HSV-2 infected men and women and the ability of samples to inhibit HSV infection will be measured. We will assess whether anti- HSV activity is associated with the concentration of antimicrobial peptides and proteins in the mucosal samples with a focus on defensins, secretory leukocyte protease inhibitor (SLPI), lactoferrin and lysozyme, mediators linked to defense against HSV infection. The results of these studies will assess the association between endogenous anti-HSV activity and resistance to HSV-2 infection in HSVneg subjects frequently exposed to HSV-2 from infected sexual partners and may lead to the rational development of strategies to prevent HSV-2 acquisition. Approximately 17% of the US adult population is infected with the virus that causes genital herpes, and currently, there is no cure for herpes and no vaccine that prevents infection or disease. Some people who are frequently exposed to the virus from infected sexual partners appear to be resistant to infection. The goal of this proposal is to determine the mechanism of this apparent resistance in order to develop strategies to prevent genital herpes.